I'm happy the gas cap doesn't fall off! If you told me it was supposed to seal I would be worried but venting is not its problem. I was suspect that the tank might have issues. After going for a ride I opened the trunk and smelled around. No issue with fumes in the trunk, and in a couple places you can see the tank. In fact the trunk didn't smell fumy at all.

I am beginning to think I had/have a combination of issues. Worn out fuel pump and hoses. Makes oil gassy and everything smelly. Many small oil leaks, main seal, valve covers etc. Probably some small exhaust leaks too. Not to mention lots of greasy build up on everything. When it all gets hot and flowing it all adds up: running rich, gassy leaking things + oily grease + exhaust = old car smell. I'm going to degrease things as much as possible and give it a good spray this weekend and change the oil now that the fuel pump is replaced. I ordered new valve cover gaskets and replaced the PVC and valve cover grommet . Hopefully that all makes things more pleasant.